During the process of production of field effect transistors, e.g., MOSFETs, plasma etching is commonly used. Low temperature gas annealing following etching often hides damage and passivates traps in the transistors without restoring long-term reliability. The effects of plasma etching or ion bombardment techniques are often monitored to determine the amount of charging damage being done to the transistors.
In a conventional method for detecting damage due to plasma etching, characteristics of the transistor(s) under test are measured. These characteristics include the threshold voltage, V.sub.t. Typically, a current of about 1 nA (nanoampere) per transistor gate or approximately 0.1 nA/square micrometer is applied for about 1 second. After application of the current, the characteristics are measured again. The process is then repeated for a predetermined period of time, such as 200 seconds.
In order to determine the changes occurring in the characteristics, typically the results of the re-measurement are evaluated periodically during the testing. By way of example, if the testing process is performed for 100 seconds, and evaluations are done every five seconds, there are twenty evaluations performed during testing with one evaluation performed following testing. If each evaluation lasts two minutes, it takes close to an hour to characterize the damage with no guarantee that the amount of damage induced by processing has been adequately identified.
With the time requirements of conventional techniques to characterize damage, monitoring cannot be performed in real-time during the manufacturing process. Thus, a need exists for monitoring of damage that produces accurate characterization of damage in a short period of time. The present invention addresses such a need.